The aims of the proposed project are to determine which sex is limiting reproduction in an insect species with paternal care, and to determine the nature of courtship roles. Parental investment and sexual selection theories argue that the limited sex should compete for access to mates and therefore be the aggressive, actively courting sex. The limiting sex, on the other hand, should be coy and highly selective of mating partners. These theories predict that in species with extensive paternal care, males are the limiting sex, and courtship roles should be reversed (i.e., females the aggessive courters, males coy and choosy). Recent models and field studies indicate that this is not always the case. This project comprises a combined field and laboratory study of a water bug, Abedus indentatus (Hemiptera), in which males carry the eggs on their backs until they hatch. Field studies will continue to monitor sex ratios, female fecundity, male clutch sizes, and environmental parameters in a natural population. Laboratory experiments are designed to: 1) determine whether either sex exhibits a significant choice of mating partners, and, if so, what the possible cues and selective advantages of mate choice are; 2)\determine whether either sex is competitive and active in courting and attracting mates; and 3) measure egg and sperm production rates and brooding rates as a function of environmental parameters. Finally, semi-natural populations will be established in very large aquaria with different operational sex ratios to quantify the conditions under which one sex limits the reproduction of the other.